I am on BT Unlimited (ADSL2+) and I can access it fine.
Try pinging your site in the command prompt.
You should see something like the following:
Pinging amersham.org.uk [18.104.22.168] with 32 bytes of data:
Request timed out.
If you see something like the following:
Ping request could not find host www.amersham.org.uk. Please check the name and
Then try ping like the following:
ping -4 www.amersham.org.uk
And if that works you have an issue with IPv4 and IPv6.
However if it fails to return that IP address then try flushing your DNS Cache by the following:
It should return the following:
Windows IP Configuration
Successfully flushed the DNS Resolver Cache.